As decentralized energy supply facilities become more widespread, specifically solar power installations, which are installed on the roofs of houses, on commercial buildings or on open ground, there is increasing awareness of the fact that, in case of a hazard such as fire or storm, or for the conduct of maintenance operations, a reliable facility must be available for the conductive parts of these installations to be made safe at any time. The accessibility or effectiveness of disconnection devices may be compromised in case of a hazard, in that preliminary damage associated e.g. with the effects of heat and smoke may preclude the reliable and sustainable action of safety measures or prevent access to tripping mechanisms. In consequence, for example, extinguishing measures on the roof frame of a burning house cannot be undertaken when there is a risk that fire fighters might be injured by the high d.c. (direct current) voltages associated with a photovoltaic installation, which may still be operational.
For the protection of persons and for the prevention of material damage by high d.c. voltages in a photovoltaic installation, DE 102005018173 proposes a device whereby the generator of the installation is short-circuited by means of a protective device that is arranged close to the generator. A disadvantage of this embodiment is the fact that the delivery of energy, to the building and consequently to an electricity grid via an inverter that is connected to the generator, is no longer possible.
Publication DE 102006060815 discloses a switching element, associated with a respective photovoltaic module, that is arranged in such a way that when the switching element is activated the associated module is de-energized. The switching element is activated by means of a high-frequency signal that is modulated on the d.c. line. In the solutions described in DE 102006060815, the delivery of energy to an electricity grid via an inverter is likewise precluded, given that, in all disclosed embodiments, the generator isde-energized. Moreover, the arrangement of a switching element at each module in a potentially multiple number of strings is associated with a not inconsiderable level of expenditure on circuitry.